Gas blocking device for optical fiber repeater

ABSTRACT

A gas blocking device is used in an optical fiber repeater or other device to prevent the passage of gas, for example, to prevent nitrogen from escaping from a pressurized housing through a fiber holding tube or pigtail. The gas blocking device includes a fiber containing body, a fiber organizing insert, and a locking member securing the insert to one end of the body. The fiber containing body is attached to one end of the fiber holding tube. The fibers extend from the fiber holding tube through a passageway in the body, and each of the fibers extends through a fiber receiving hole in the fiber organizing insert. The insert engages the body such that the insert is prevented from rotating with respect to the body and the fibers are protected against microbending and other damage. A material, such as hot melt glue, fills at least a portion of the body and surrounds the fibers to block the gas from entering the fiber holding tube.

TECHNICAL FIELD

The present invention relates to fiber optic systems and, moreparticularly, to a gas blocking device used to permit the passage ofoptical fibers while preventing the passage of gas therethrough.

BACKGROUND INFORMATION

Repeaters are commonly used in fiber optic systems to amplify opticalsignals being transmitted over long distances. A repeater body iscoupled to a fiber optic cable at each end. The repeater body houseselectronic circuitry and lasers used to amplify the optical signals.Lasers and electronics housed in the repeater body should be maintainedunder very dry conditions, because the slightest amount of condensationin the repeater can cause arcing. Arcing can be devastating to theoperation of the system. Maintaining these very dry conditions is mostimportant in undersea applications but also applies as well toterrestrial applications.

To achieve these dry conditions, prior to installation, the repeaterhousing is vacuum drawn and the air is replaced with pressurizednitrogen to prevent moisture from entering the repeater housing. Toenable the repeater housing to maintain the pressurized nitrogen, it isconventional to route optical fibers entering and exiting the repeaterthrough a seal. One known system for creating the seal includes routingthe fibers through a plastic tube on the outside of the repeaterhousing. A compressible rubber stopper is then inserted in one end ofthe plastic tube to seal the end of the plastic tube. The rubber stopperis punctured one hole at a time for each optical fiber in the bundle andeach fiber is routed through a respective hole during the puncturingprocess. The compressible nature of the rubber stopper is intended tocreate an individual seal with each optical fiber. At least one drawbackof this conventional seal and sealing method is that the assembly islabor intensive.

Additionally, this type of sealing assembly is better suited for waterblockage. Because the sealing assembly relies on a friction fit betweenthe rubber stopper and the plastic tube and fibers, the nitrogen in thepressurized housing interior could still potentially escape through theseal if tight tolerances are not achieved. Furthermore, this existingsealing assembly had difficulty accepting more than eight fibers due tothe inherent material properties of the rubber stopper and thedifficulty in drawing the fiber through the rubber. This sealingassembly thus could not easily accommodate the increased number offibers in high fiber count cables.

Accordingly, there is a need for a gas blocking device that is easier toinstall, that has improved sealing properties, and that is capable ofaccommodating an increased number of fibers.

SUMMARY OF THE INVENTION

In accordance with the present invention, an optical fiber device isprovided. The optical fiber device comprises a housing that is vacuumdrawn and pressurized with a gas to prevent moisture from entering thehousing. An optical fiber holding tube extends through a wall in thehousing such that a first end of the optical fiber holding tube iscontained in the housing and a second end of the tube is located outsidethe housing. A plurality of optical fibers extends from the first end ofthe optical fiber holding tube to the second end of the optical fiberholding tube without interruption. A gas blocking device is attached tothe first end of the optical fiber holding tube. The optical fibersextend through the gas blocking device and are surrounded by a material,creating a seal that prevents the gas from passing through the opticalfiber holding tube.

In accordance with another aspect of the present invention, a gasblocking device is provided for use with an optical fiber holding tube.The gas blocking device comprises a fiber containing body having apassageway for receiving a plurality of fibers from the optical fiberholding tube. A material, such as hot melt glue, at least partiallyfills the passageway of the fiber containing body and surrounds theplurality of fibers passing through the passageway. A fiber organizinginsert is secured at one end of the fiber containing body and has aplurality of fiber receiving holes for receiving respective ones of theplurality of fibers. The fiber organizing insert and the fibercontaining body preferably include cooperating key structures such thatthe fiber organizing insert is prevented from rotating with respect tothe fiber containing body. A locking member preferably secures the fiberorganizing insert to the one end of the fiber containing body.

In one embodiment, the passageway within the fiber containing bodyincludes a wide portion, a narrow portion, and a tapered portion betweenthe narrow portion and the wide portion. The narrow portion of thepassageway preferably has an inside diameter dimensioned such that thefibers act as strength members within the material in the narrowportion. For example, the ratio of the cross-sectional area of thefibers to the cross-sectional area of the narrow portion is about ½. Thefiber organizing insert is secured within the wide portion of thepassageway and is preferably made of a substantially non-compressiblematerial.

In accordance with a further aspect of the present invention, the gasblocking device is provided as an assembly comprising the fibercontaining body for receiving the fibers and the material, the fiberorganizing insert adapted to be positioned at one end of the fibercontaining body, and the locking member adapted to lock the fiberorganizing insert to the fiber containing body.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reading the following detailed description, takentogether with the drawings wherein:

FIG. 1 is a schematic view of one end of a repeater, including a gasblocking device according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view of the gas blocking device includingfibers and material, according to one embodiment of the presentinvention

FIG. 3 is a perspective view of the gas blocking device shown in FIG. 2;

FIG. 4 is a perspective view of the fiber organizing insert, accordingto one embodiment of the present invention;

FIG. 5 is a top plan view of the fiber organizing insert shown in FIG.4; and

FIG. 6 is a perspective view of the fiber containing body used in thegas blocking device shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The gas blocking device 30, FIG. 1, according to the present invention,is used to substantially prevent or block the passage of gas whileallowing optical fibers to pass through. According to the exemplaryembodiment, the gas blocking device 30 is used in an optical fiberrepeater 10. The gas blocking device 30 may also be used in otherdevices that house optical fibers, such as a joint box.

The repeater 10 receives, amplifies, and retransmits signals beingcarried by a fiber optic cable. Repeater 10 includes a repeater housing12 containing a signal processing and routing system 14 having a laser(not shown). An end cover or wall 20 covers the end of the repeaterhousing 12, and a cone 16 encloses the end of the repeater housing 12.An optical fiber holding tube 18, sometimes referred to as a pigtail,extends from inside the repeater housing 12 through the end cover 20 andout of the cone 16. A tube seal 22 is incorporated where the fiberholding tube 18 extends through the end cover 20 to make the repeaterhousing 12 water tight in that area.

A cable structure (not shown) is connected to the cone 16, and opticalfibers 24 extend from the cable structure through the optical fiberholding tube 18 to carry signals to and/or from the repeater 10. Thefibers 24 exit the end 26 of the optical fiber holding tube 18 within afiber tray 28 inside the repeater housing 12 and are coupled in a knownmanner to the signal processing and routing system 14. A similararrangement exists at the other end of the repeater 10. This enables thesignals transmitted by the fibers 24 to one end of the repeater 10 to bereceived, amplified and retransmitted to the fibers 24 at the other endof the repeater 10.

To prevent moisture or condensation from entering the repeater housing12, the repeater housing 12 is vacuum drawn and the air is replaced withpressurized nitrogen or another suitable gas. The repeater housing 12 istypically pressurized to about 30 to 35 psi. The gas blocking device 30is attached to the end 26 of the optical fiber holding tube 18 inside ofthe repeater housing 12 and prevents the pressurized gas from exitingthe repeater 10 through the optical fiber holding tube 18. The gasblocking device 30 also prevents gas from entering the repeater 10through the fiber holding tube 18.

According to one embodiment, the gas blocking device 30, FIGS. 2 and 3,includes an elongated fiber containing body 32, a fiber organizinginsert 34, and a locking member 36. The fibers 24 extend through thefiber organizing insert 34 into a passageway through the body 32 at oneend and pass out of the body 32 through the opposite end. The lockingmember 36 secures the fiber organizing insert 34 to the body 32. Amaterial 40, such as hot melt glue, surrounds the fibers 24 within thebody 32 and seals the passageway around the fibers 24, therebypreventing gas from passing through the body 32. Hot melt glue has thepreferred capability of being re-heated and softened to allow adjustmentof the fibers 24 within the body 32 as needed. Other types of material,such as epoxy or other adhesives, may also be used.

In one embodiment, the passageway in the fiber containing body 32includes a wide portion 42, a narrow portion 44, and a tapered portion46 therebetween. The wide portion 42 and tapered portion 46 allow thematerial or adhesive 40 to flow into the narrow portion 44 of thepassageway where the sealing takes place. The fibers 24 preferably actas strength members within the material 40 similar to the manner inwhich steel is used to reinforce concrete. For example, when the gasblocking device 30 is frozen, the fibers 24 hold the adhesive 40together and prevent the adhesive 40 from cracking. To allow the fibers24 to act as strength members and provide this reinforcement, the narrowportion 44 of the passageway should not be too wide. The narrow portion44 preferably has an inside diameter just large enough to receive thefibers 24 and to allow the material or adhesive 40 to flow into thenarrow portion 44 and seal the fibers 24. The ratio of thecross-sectional area of the fibers 24 to the cross-sectional area of thenarrow portion 44 is preferably about ½. In one example, the narrowportion 44 may have an inside diameter of about {fraction (1/16)} in.This size is capable of accommodating about 16 to 24 fibers 24. Althoughonly four fibers 24 are shown in FIGS. 2 and 3 for purposes of clarity,it is contemplated that multiple fibers may be used, for example 16 to24 fibers or perhaps even more.

The adhesive 40 preferably fills at least substantially the entirelength of the narrow portion 44 of the passageway. The narrow portion 44preferably has a minimum length sufficient for pressure sealingpurposes. In the exemplary embodiment, the length of the narrow portion44 is about 1.5 in. Although the exemplary embodiment is shown with aspecific shape, the fiber containing body 32 can have other shapes,sizes and configurations.

According to one preferred embodiment, the fiber organizing insert 34,FIG. 4, has a center plug 50 and a seating flange 52 that seats thefiber organizing insert 34 relative to the fiber containing body 32(FIG. 2). The fiber organizing insert 34 includes preformed fiberreceiving holes 54 through which the individual optical fibers 24 extendand enter into the fiber containing body 32. Although the exemplaryembodiment shows the holes 54 arranged as a single circle, the preformedfiber receiving holes 54 can be arranged in two or more concentriccircles to accommodate additional fiber 24.

The fiber organizing insert 34 is preferably made of a rigid,substantially non-compressible material, such as plastic, that will notscratch or damage the fibers and will withstand being heated and frozen.The fiber organizing insert 34 is thus capable of accommodating morefibers than the compressible rubber stoppers used in the conventionalsealing devices. Although plastic is used in the exemplary embodiment,other suitable materials may also be used. The fiber organizing insert34 may also have other shapes, sizes and configurations.

The fiber organizing insert 34 engages the fiber containing body 32 suchthat the seating flange 52 is seated at the end of the fiber containingbody 32 and the center plug 50 extends into the wide portion 42 (seeFIG. 2). The fiber organizing insert 34 and the fiber containing body 32preferably include cooperating key structures for preventing rotation ofthe fiber organizing insert 34 with respect to the fiber containing body32. By preventing rotation when the fiber organizing insert 34 isengaged with the fiber containing body 32, the cooperating keystructures prevent undesirable twisting of the fibers 24. The fiberorganizing insert 34 thus organizes and restrains the fibers 24 toprevent microbending and other damage to the fibers 24.

According to the exemplary embodiment of the cooperating key structures,shown in FIG. 5, a locking key 56 on the fiber containing body 32engages a locking recess 58 in the seating flange 52 of the fiberorganizing insert 34. The locking key 56 preferably extends from the endof the fiber containing body 32, as shown in FIG. 6. The fiberorganizing insert 34 preferably includes multiple locking recesses 58 tofacilitate positioning of the fiber organizing insert 34.

Although one embodiment of the cooperating key structures is shown anddescribed, any arrangement of cooperating key structures capable ofpreventing rotation may be used. For example, the fiber organizinginsert 34 may include a single locking recess 58 or the fiber containingbody may include multiple locking keys 56. Alternatively, the fiberorganizing insert 34 may have keys or projections engaging recesses inthe fiber containing body 32.

The fiber organizing insert 34 is secured against the fiber containingbody 32 by the locking member 36 (see FIG. 2). The locking member 36includes an inner extending flange 60 extending over the end of the body32 and a base 62 extending around the outside of the body 32. The base62 of the locking member 36 is secured to the fiber containing body 32,for example, by a threaded engagement. According to the exemplaryembodiment, the base 62 has a shaped portion 64 (e.g., hexagonal) thatmay interface with a tool, such as a wrench. The locking member 36 mayalso be attached to the fiber containing body 32 in other ways. When thelocking member 36 is secured to the body 32, the inner extending flange60 bears against the fiber organizing insert 34 to effectively sandwichthe fiber organizing insert 34 between the locking member 36 and thefiber containing body 32.

To assemble the gas blocking device 30, the fiber containing body 32 issecured to the end 26 of the fiber holding tube 18. The fiber containingbody 32 and the fiber holding tube 18 are it both preferably made ofcopper and may be secured by soldering. Although copper is preferredbecause of its good conductability, other materials may also be used.The fibers 24 are inserted into the fiber organizing insert 34 and thefiber containing body 32. Each of the fibers 24 is inserted through oneof the fiber receiving holes 54 in the fiber organizing insert 34.

With the fiber organizing insert 34 positioned just above the lockingkey 56 of the fiber containing body 32, the hot melt glue (or othersuitable adhesive) is injected into the fiber containing body 32 untilthe hot melt glue substantially fills the narrow portion 44. The fiberorganizing insert 34 is then moved into place such that the locking key56 engages one of the recesses 58. The locking member 36 is thenpositioned over the fiber organizing insert 34 and threaded onto thefiber containing body 32 to secure the fiber organizing insert 34 to thebody 32. The fiber holding tube 18 with the gas blocking device 30 isthen installed into the repeater housing 12 with the gas blocking device30 and fibers 24 exiting the gas blocking device 30 being stowed in thefiber tray 28.

Accordingly, the gas blocking device of the present invention isrelatively easy to install and is more effective at blocking gascompared to conventional sealing devices.

Modifications and substitutions by one of ordinary skill in the art areconsidered to be within the scope of the present invention, which is notto be limited except by the claims that follow.

What is claimed is:
 1. An optical fiber device comprising: a housinghaving a wall, wherein said housing is vacuum drawn and pressurized witha gas to prevent moisture from entering said housing; an optical fiberholding tube extending through said wall and having a first end and asecond end, said first end of said optical fiber holding tube containedin said housing and said second end of said optical fiber holding tubelocated outside of said housing; a plurality of optical fibers extendingfrom said first end of said optical fiber holding tube to said secondend of said optical fiber holding tube without interruption; and a gasblocking device attached to said first end of said optical fiber holdingtube, wherein said gas blocking device comprises: a fiber containingbody having a passageway, said passageway including a wide portion and anarrow portion, wherein said optical fibers extend through saidpassageway in said fiber containing body of said gas blocking device;and a sealing material contained in said passageway and hardened aroundsaid optical fibers within said passageway such that said gas blockingdevice creates a seal substantially preventing gas from passing throughsaid optical fiber holding tube, and wherein said plurality of opticalfibers act as strength members that reinforce said sealing materialwithin at least said narrow portion of said passageway.
 2. The opticalfiber device according to claim 1, wherein said gas is nitrogen.
 3. Theoptical fiber device according to claim 1, further including a waterseal sealing an interface between said wall and said optical fiberholding tube extending through said wall.
 4. The optical fiber deviceaccording to claim 1 wherein said gas blocking device includes: a fiberorganizing insert secured within said wide portion of said passageway atone end of said fiber containing body such that said fiber organizinginsert is prevented from rotating with respect to said fiber containingbody, wherein said fiber organizing insert includes a plurality of fiberreceiving holes each receiving respective ones of said plurality offibers.
 5. The optical fiber device according to claim 4, furtherincluding a locking member securing said fiber organizing insert to saidone end of said fiber containing body.
 6. The optical fiber deviceaccording to claim 4, wherein said passageway in said fiber containingbody includes a tapered portion between said wide portion and saidnarrow portion.
 7. The optical fiber device according to claim 4,wherein said fiber organizing insert is made of a substantiallynon-compressible material.
 8. The optical fiber device according toclaim 4, wherein said fiber containing body and said fiber holding tubeare made of a conductive metal and are soldered together.
 9. The opticalfiber device according to claim 1, wherein said sealing material is hotmelt glue.
 10. The optical fiber device according to claim 1 wherein theratio of the cross-sectional area of said fibers to the cross-sectionalarea of said narrow portion is about ½.
 11. A method of passing opticalfibers into a pressurized housing, said method comprising the steps of:securing a gas blocking device to one cud of an optical fiber holdingtube; inserting a plurality of optical fibers through said optical fiberholding tube and through said gas blocking device; injecting a sealingmaterial into said gas blocking device, wherein said sealing materialsurrounds said optical fibers and hardens such that said optical fibersact as strength members reinforcing said sealing material and such thatsaid material creates a seal substantially preventing gas from passingthrough said optical fiber holding tube; and installing said opticalfiber holding tube and said gas blocking device into said housing suchthat said fibers exit said gas blocking device into said housing. 12.The method of claim 11 wherein the stop of injecting said sealingmaterial includes injecting an adhesive.
 13. The method of claim 11wherein the step of injecting said sealing material includes injecting ahot melt glue.
 14. The method of claim 11 further comprising the stepsof: inserting each of said optical fibers through a hole in a fiberorganizing insert; and securing said fiber organizing insert to said gasblocking device.